This study will investigate the role of unrecognized PID in the development of tubal factor infertility over a four year period. 1500 women at risk for PID will be enrolled in this prospective study, and those with unrecognized PID, as defined by endometrial histology, will undergo a hysterosalpingogram 12 weeks after enrollment to document tubal patency. Participants will be contacted by telephone every three months for at least one year to monitor for reproductive events. A large body of retrospective data associate tubal factor infertility with prior unknown or silent upper genital tract infection. The proposed study will be the first prospective trial to comprehensively study the microbiology and histology of unrecognized PID, and its impact on fertility.